Forest Health Hot Topics

The Division of Forestry and our cooperators have several ongoing projects related to the insects listed below. These projects include both aerial and ground-based surveys, the results of which are summarized yearly in the Forest Health Conditions in Alaska  report produced by USDA Forest Service - Forest Health Protection and their partners. Please refer to the referenced report for details on the current status of the following insects.

 

Bark Beetles - Spruce beetle (Dendroctonus rufipennis) and the northern spruce engraver (Ips perturbatus) are the two major spruce-killing bark beetles in Alaska’s forests. Both are native and occur throughout the forests of the state.

 

D. rufipennis - S. Valley, ODF, Bugwood.jpg

Spruce beetle
Actual size: ~1/4 inch
S. Valley, OR Dept of Ag
Bugwood.org

Spruce beetle is always present in our spruce forests and has a notorious history in Alaska. In times of low populations, spruce beetle favors large diameter, wind-thrown or otherwise damaged spruce trees. Spruce beetle is capable of killing otherwise healthy spruce, though, when populations are high. Long-time residents may remember the spruce beetle outbreak in the 1990s. At the peak of the outbreak, in 1996, spruce beetle-caused tree mortality was observed on more than one million acres.

Since 2011, observed spruce beetle mortality statewide had been relatively low. Recent surveys, however, detected a dramatic increase in spruce beetle activity in several areas of Southcentral Alaska.

 

Spruce beetle management options for home and woodlot owners
(University of Alaska Fairbanks – Cooperative Extension Service)

Spruce beetle Forest Insect and Disease Leaflet (Contains Forest Management Options)
(www.barkbeetles.org)

 

 

 Ips perturbatus - Pest and Diseases Image Library, Bugwood.jpg

Northern spruce engraver
Actual size: ~3/16 inch
Pest and Disease Image Library
Bugwood.org

Spruce beetle damage is typically less extensive in Interior Alaska. There, the northern spruce engraver is commonly observed causing damage to spruce. From May through July, northern spruce engravers actively attack white spruce weakened by wind, fire, flooding, or other stressors. Fresh cut spruce and spruce slash from land clearing or forest management activities may also be susceptible. 

Northern spruce engraver populations are being closely monitored in the Tanana River valley. A 2012 windstorm in that area left large areas of spruce blown down, broken, or leaning. Increased amounts of northern spruce engraver-caused white spruce mortality have been observed in these wind-impacted forests recently. 

 

Northern spruce engraver Forest Insect and Disease Leaflet

 

 

Spruce Aphid - The non-native spruce aphid primarily infests Sitka spruce as well as ornamental spruce in coastal areas. While some trees may be killed in severe infestations, most affected trees survive. Aphid-caused defoliation can weaken trees, potentially making them more susceptible to other forest health threats.

The current known range of spruce aphid in Alaska includes Southeast Alaska, Prince William Sound, the Kodiak Archipelago, and the Kenai Peninsula. 

 

Integrated Pest Management Issues - Spruce aphid
(University of Alaska Fairbanks – Cooperative Extension Service)

Spruce aphids
Alaska Division of Forestry

20160225 - Spruce aphid homer - J. Moan AKDOF (6).JPG

 

Generalist defoliators - Generalist defoliators refers to insects that feed on the leaves or needles of a wide variety of tree and plant species. Alaska is home to several species of native moths whose larvae are considered generalists in their feeding habits. Occasionally, these moths can outbreak, causing widespread defoliation.

20150802 (06) - SC ADS - DAMAGE - Extensive defoliation in upper Yentna area - J.Moan DOF.JPG

Defoliated willow, alder, and birch
Upper Yentna River valley
Alaska Division of Forestry

Recent aerial surveys noted ongoing generalist defoliation in several areas. This defoliation is occurring in parts of the Alaska Range, Aleutian Range, and multiple locations in Southwestern Alaska. Recent evidence suggests that the native moth, Orthosia hibisci,is responsible for the defoliation in at least some of the impacted areas. DNA-based investigations into the insect or insects responsible will continue.

 

For more information, please contact:

Jason Moan, Forest Health Program Manager
DNR Division of Forestry, Anchorage